MESSUNG SERVO & MOTION CONTROL AUTOMATION FOR VFFS MACHINES
Vertical Form, Fill, and
Seal (VFFS) machines are used in the consumer products industry for a wide
variety of packaging applications. Various products like salt, tea, sugar,
spices, snack foods, wafers, detergent, candies, milk, sauce, etc. are placed
into formed pouches and then sealed. The pouch material is flexible and
typically heat-sealable plastic. Paper is also used and sealed by glue.
The VFFS machine can be divided into
four functional areas:
1. Mixing, Weighing, Dosing
2. Forming
3. Feeding, Aligning,
Registration
4. Closing, Sealing, Cutting.
Typically,
Fully automatic VFFS
machines require limited operator intervention. The operator need only
replenish product by loading supply hoppers or changing packaging film drums.
For machines that are semi-automatic, operators are required to perform part of
the packaging operation.
VFFS machines can be intermittent or continuous motion. Intermittent motion machines operate on the
principle that vertical bag seals are made when the film is moving and
horizontal seals occur when the film stops. Intermittent motion machines offer
a suitable solution for applications where speed is not absolutely paramount.
Continuous motion machines operate on the
principle that both vertical and horizontal bag seals are made when the film is
in motion. These machines operate at the highest attainable speeds and require
a reciprocating sealing jaw motion format.
There are two major process advantages for a continuous motion
machine over an intermittent type:
• Faster cycles times. On a continuous motion machine the cross
jaw moves with the film and can perform the horizontal sealing application
while the film is still moving. The typical intermittent machine operates at 60
to 80 packs per minute (ppm) maximum, while a continuous machine can operate up
to speeds of 180 ppm. The highest machine speed attainable is determined by the
weighing mechanism.
• Control over the cross jaw
along the vertical plane provides additional bag making possibilities.
Generic VFFS Machine Process
A roll of film is unwound
and formed into a tube over a forming collar. A vertical overlap seal is
applied to the tube by the vertical sealing bars. A bottom seal is created by
the horizontal sealing bars in the cross jaws.
The formed pouch is then
filled with correct amount of product while the film tube is being fed by the
film transport belts. Often a precision scale or an auger ensures that the
proper amount of product is placed in the pouch in a consistent manner.
After the correct length of
film tube has been fed, a top seal of the filled pouch is created by the
horizontal sealing bars, while the filled pouch is cut from the descending film
tube by a knife in the cross jaws.
If the film is pre-printed, a registration
sensor is added to the system to correct the film position in order to maintain
the correct print position relative to the end of the pouch. The bottom seal
creation of the empty pouch, top seal creation of the filled pouch and cutting
of the filled pouch all occur at the same time.
1. Film Unwind
Film unwind is responsible for unwinding film
into the machine, providing operator ease-of-splice (optional), roll change-out
features (optional) and film tension. Many unwind sections are static mandrel
(un-powered) types and use either a pneumatic brake or friction brake to
control unwind action and provide applicable film tension. Although,
occasionally the unwind mandrel will require VFD, Servo or DC gear motor type
control.
In the unwind section often there are roll
change features, such as dual mandrels, roll lifts and vacuum splice bars. A
vacuum splice bar is a horizontal bar with a vacuum manifold built in and a
small horizontal slot (suitable to accommodate a utility knife blade) through
the middle of the bar. The unwind section will also include the film tension
and / or dancer. The dancer can provide a speed feedback (analog or discrete)
to the unwind control circuit, as well as a film accumulator area for bag index
purposes, especially on an intermittent type machine. Additional options possible
for the unwind section are functions like zipper applicators and breather
inserters.
1. Film Registration
This section includes the film registration sensor and placement
adjustment mechanisms. The film registration is used on film with graphics or
pre-printed information. Printing process variations, film stretch, film
slippage during acceleration and other factors can allow the graphics to drift
away from ideal cosmetic / marketing placement on the finished bag. The
registration mark provides a method to make minor adjustments to the actual end
placement of the seal and cut on a bag. When there is no printing or graphics
on the bag, the process is defined solely on length. Also located in the film
registration section, it is common to have the film alignment / tracking
adjustment mechanisms. These are used to ensure the film stays in the correct
place on the forming tube.
1. Forming Tube
The forming tube mechanics are often unique
designs for different machines, films and products. However, the general
description is an inverted cone with radius corners. This cone and the correct
diameter tube (shapes can differ from round for special package needs) are
combined to form the flat film into a tubular or tunnel type shape, which ends
up being wrapped around the external surface of the actual forming tube. In
order to provide extra film for the long or "back" seal, the width of
the film will be greater than the circumference of the forming tube. The long
seal is formed by several different heater mechanical configurations that are
typically placed on the front of the forming tube and are eight to twelve
inches in length. Linear film speed and type are factors in determining the
correct minimum length of the long seal. There are two main types of long seal.
The first type of long seal is the static bar, which is a heated
bar with heating element and thermocouple. This bar will be engaged into the
film and forming tube only while the film is in motion with slight timing
delays to prohibit melting of the film when stationary. There can also be two
bars, but placed where they are facing one another in a manner to allow the
long seal flaps to be placed in between the two bars. This method is used
instead of the overlapping method used for single bar configurations. This can
provide stronger seals / seams and the product ambient temperature (i.e.
forming tube temperature) will have less of a factor on the loop control.
The second type of long seal is the dynamic belt, a single-heated
stainless steel belt with two pulleys. A heated plate transfers the heat to the
stainless steel band or belt and is engaged into the film and forming tube
while the film is in motion. Like the static bar type, there can also be dual
dynamic belts / bands. The benefit of dynamic belts is they can move with the
film and also be adjusted to operate faster than the base film speed or even
slower. These are process decisions made based on many product, machine and
material factors.
1. Film Pull Belt(s)
There are typically two film pull belts - right
side and left side. They are typically vacuum belts, which allows for better
gripping control in dusty, high moisture or cold operating environments. The
belt mechanics are often powered by VFD motors with encoder feedback, servo
axes or perhaps stepper motors. Occasionally there will be only one motor that
is mechanically transferred to the separate belts, but the general practice is
to eliminate the additional special mechanical costs in lieu of the additional,
but more flexible, controls cost. The film pull belts provide the actual force
to pull the film through the machine and are used to maintain good film tension
on the forming plow and tube. Often code is used to monitor position and
velocity error to ensure that slight mechanical differences are not allowing
one side to pull more than the other.
1. Cross (Sealing) Jaw
The cross jaw is responsible for three major functions—to seal the
top of the previously filled bag, to create the bottom seal for the soon to be
filled bag and to cut or separate the completed bag from the bottom of the new
bag.
The front and back cross jaws operate as a pair. The front and
back jaw will both have a top seal area (horizontally) and a bottom seal area.
Additionally, either the front (typically due to maintenance reasons) or the
back jaw set will have a knife which runs horizontally in the middle of the jaw
face. This knife is recessed and is activated by a pneumatic actuator. The
opposite jaw set will contain the anvil for the knife.
Each jaw will have one or two heating
elements as well as a thermocouple for temperature control. Additionally, the
cross jaw section can have options like product wipers, bag deflators, bag
hanger punch, gusset (single & double) creation mechanics and flat bottom
bag mechanics to name a few. Cross jaws are typically configured mechanically
where the front and back jaws interpose each other and therefore meet in the
vertical centerline of the bag and forming tunnel. However, there are also versions
where either the front or back jaw is stationary and the opposite jaw is
moveable. Servo drive/motor combinations, VFD drives with induction motors and
high power pneumatic cylinder actuators are used to close the jaws and provide
the necessary sealing pressure to provide a suitable bag seal. It is very
common for the jaws to contain built-in springs to allow for some closure error
as well as a default force. Often, position and torque data are monitored for
the cross jaws. This data can easily be used to detect product in the seal or
between the jaws. Anytime there is product in the seal, these two bags should
be discarded due to potential seal / seam leakage.
The previous sections are typical for an intermittent VFFS
machine; however a continuous machine will often contain a section called the
rotary or vertical jaw, depending on the bagger type.
1. Rotary Jaw
The first type of continuous bagger is the rotary / "D" jaw. For a rotary type bagger, the horizontal plane motion for the front and back cross jaws is replaced with a rotary type motion. This is accomplished with special mechanisms, orbital gearboxes and/or four-bar type linkages. In general each jaw is attached between two gears. Each jaw end gear is actuated by a driving gear. Along with some orientation linkages, these jaws will operate in a “mirrored” fashion so the jaws maintain the same distance to the vertical plane as they rotate in a top-to-bottom and around fashion. The main benefit of a continuous type bagger over the intermittent is that since the cross jaw is now moving along the vertical plane as well as the horizontal plane, the sealing process can occur without stopping the film completely.
1. Vertical Jaw
The second type of continuous bagger is the
box or square jaw type. This differs from the rotary jaw in that there are now
two mechanical movers for the overall cross jaw - one is the horizontal-only
plane and the other is for the vertical-only plane. Although this adds
increased controls and mechanical costs, it can also provide additional bag
making process options, longer bags with fewer constraints and more control for
product sweeping type functions. Mechanically, the cross jaw mechanics and
motor are contained on a carriage. This carriage is controlled and moved along
the vertical plane via the vertical mechanics and motor.
v Machine Speed
The speed of the VFFS
machine is the rate at which it is able to (1) form the pouch (bag, sachet,
etc.); (2) fill it with product; (3) seal it; (4) cut it; and (5) transfer the
package for shipment or further end-of-line packaging such as a case packer,
over wrapper etc. The speed of the machine is one of the main attributes in
many end users’ buying criteria. Machine builders will design their machines to
operate at the highest speed possible.
v Challenges
1.
How to
design the mechanics of the machine to operate at high speed and maintain the
correct tension of the film feed in order to maintain the quality of the packaging.
2.
How to
position the film accurately based on eye mark registration.
3.
How to
design the optimum sequence of machine operation.
Refer to the timing diagram below for an example of a Form, Fill
and Seal operation in intermittent duty cycle. This is an example of typical
VFFS machine with an auger screw filling system.
v Filler
Types:
1.
Auger: Auger is screw feeder generally driven by Servo Motor. Motor Rotation
defines material loaded in the Pouch. This is suitable for Powder, Grains,
Chips.
2. CUP Feeder:
This is Multi-head feeder. Suitable for high speed Machines, where the material is ready to be dropped. This is also equipped with weighing mechanism. It has separate control mechanism which handshakes with Machine Controller. This mechanism also supports both volumetric & weigh feeding.
3. Piston type Feeding:
This is suitable for generally Liquid and viscous material like sauce, jam. Piston is driven by Servo Motor. Suction stroke is used for loading the material and Discharge for dispensing it in the Sachet. It has suction and discharge valves.
v End Users expect VFFS to be:
1.
Productive:
Optimize packaging process to achieve maximum
possible machine speed; maximize throughput with highest quality; high accuracy
and shorten recovery time.
2.
High
performance: Satisfy
strict accuracy requirements at high machine speeds and variable bag lengths.
3.
Flexible:
Release the burden of manual adjustment of
film registration sensor position by introducing software adjustment scheme;
improve changeover time.
4.
Easy
to use: In spite of machine
complexity, machines must be easy to maintain and operate.
v Machine
Builders expect VFFS to be:
1.
Modular
and scalable: Mix and
match VFFS machine functions that are ideally suited for specific customer
applications; customized functions to develop a new machine that is localized
to market demands.
2.
Standard: Develop and document mechanisms common to
VFFS machines that can be easily redeployed with minimum modifications, despite
different machine sections/conditions that result in more complicated
sequencing and interlocking, so that machine design and development time can be
reduced.
3.
Cost-effective:
Machine integration, mechanical, electrical
optimization and wiring start up time costs are reduced.
v Our
Sigmatek Solution:
1. S-Dias CPU CP112 with Varan Port, Ethernet
Ports, with modular construction
is best fit above application.
2. Varan Port supports Motion and I/Os.
3. Lasal Class Engineering Platform.
4. Safety CPU Enhancement.
v VARAN Bus:
1.
HARD
REAL-TIME Bus cycle times under 100 µs / Jitter less than 100 ns
2.
FLEXIBLE
NETWORK TOPOLOGIES Modular machine design with star, line, tree topologies
3.
SIMPLE AND
ECONOMIC Protocol completely implemented in the hardware, use of inexpensive
FPGAs for managers and clients
4.
OPEN
STANDARD The manufacture-independent VARAN Bus User Organization holds the rights
to the open technology
5.
AND MUCH
MORE Automatic addressing, Direct Access, multi-manager capable, CanOpenimage
ENGINEERING TOOL - LASAL
- Object-oriented programming and project
design
- Visualisation
- Drive technology
- Safety configuration
- Tools for service, remote maintenance,
updates and data exchange
HOT FACTS
ALL-IN-ONE
- ONE
toolset for all development phases; short time-to-market
OBJECT-ORIENTED
- High
modularity and reusability
GRAPHIC
REPRESENTATION - High clarity
READY-TO-USE
FUNCTION COMPONENTS - Reduce software development up to 70%
MOTION CONTROL
High-performance, flexible & economic
complete solution
for highly dynamic and exact servo applications: drives, motors,
gears, software
All configuration data and parameters
centrally in the control-
initial start-up, service and exchange simplified
Perfect communication connection to the CPU via real-time
Ethernet VARAN bus
HOT FACTS
COMPACT DRIVES - save space in the control cabinet
COMFORTABLE - library with predefined motion templates
FLEXIBLY - control different motors, standard feedback systems
ABOUT MESSUNG SERVO & MOTION CONTROL
AUTOMATION
Messung is Master Distributor – India for
Sigmatek, Austria. Together, Messung-Sigmatek deliver fully integrated,
future-oriented servo & motion
control solutions in India, incorporating programmable logic controllers,
motion control systems, drive products, HMIs and SCADA, and much more - to
bring flexibility, consistency and long-term availability for packaging
machines.
Messung is the pioneer of the PLC, one of the
leading PLC automation companies inIndia, providing cutting-edge industrial
automation & control solutions. With four decades of experience in the
industry and a history of continuous innovation, global partnerships and
pro-active R&D, Messung is the ideal partner for machine automation & control solutions in India.
Messung partners with packaging machine builders to
create tailored solutions that enhance the performance and value of their
machines. Messung’s automation andcontrols solutions can help automate single machines or complete factory
lines, ensuring operational accuracy, repeatability and stability.
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